2020-22 KTM 250 - 390 Adventure Bike Build

Above is a 2020 KTM 390 Adventure.  After buying it and riding it stock, down the roads and out in the dirt and the bumps, I can honestly say it's a big dumb pig pig.  Slow and heavy.  Totally reminds me of buying the first Honda CRF 250 L, that came into Arizona, and developing it.

When I rode the 250L, outside of the dealership, I wanted to ask them to take it back and see if I could have my money back.  Thing was, I bought it because a great price point at $5000 or whatever it was then. I also knew, that after I figured out the performance kit for it, that it would be totally different. And it worked. That bike weighed 300 lbs and had 18 hp stock. We got some weight off and got the power to 26 and it was a whole new bike.  Honda sold a bunch of bikes and we sold a bunch of kits.

This new 390 KTM is the same kind of thing.  It's on the heavy side, but some weight can come off.  It feels odd and wrong, as far as ergonomics go. Especially for control in the dirt. But that can be fixed.  And finally it needs more power, get up and go and some reliability.  And we can definitely fix that.


     As we started taking apart this bike, we realized how heavy the battery was.  For about $100, you can loose a whole 6 lbs by going to a good lithium battery.  This is high centered weight you feel. It's a must do

     The people who design the best performance products ( us and just a few others ) know darn well to take measurements of stock componets first.  On a fuel injected bike, the fuel pressure is so, so critical to performance and even maintaining stock running condition.  The running pressure of the stock bike is 54 psi. If the pressure falls below this, then starting and acceleration will suffer.  The lower it goes, the worse performance gets.   

     The next big parameter, that's super critical to know, on a fuel injected bike, is the air / fuel ratio.  Now on this particular  bike, it has an Oxygen sensor welded in the head pipe to make what we call a "closed loop" injection system.  This means that the O2 sensor feeds back information to the ECU ( electronic control unit ). This means that the system tries to make adjustments to the fuel amount to the injector, so that the pre determined air/ fuel ratio is kept.

    In the case of this bike, the pre determined air/ fuel ratio, seems to be 14.7 :1.  That's what the gauge we hooked up to shows.   When you ride down the street, the gauge fluctuates a bit, but it centers around 14.7.

    When you crack the gas, there is a bit of an accelerator pump kick in, but not a lot.  It shoots to 13.5 :1, which is a bit richer to aid in the "get up and go", but then goes right back to 14.7.

    This is important to know. Because we need to know how far you can go with opening up exhaust and intake flow, before the ecu can't adjust anymore and the bike starts to lean out.

Now that a few parameters and notes, on how it's running are taken, lets go ride it.   The first thing you may notice, is that it's an odd feeling bike, when you are riding it. Especially offroad.


     You'll definitley want to remove the rubber inserts from the footpegs. That done by removing the bolt under the bottom of the peg.  Then at least you feet will be in a better position for using the foot controls.

     After that, you'll really be in a better riding position if you use these bar risers we have, to get the bars up higer and further back.  You can see the black piece sitting on the tank above, which is the bar riser we have for use with the stock handlebars.  These move the stock bars up 3/4" or 19mm and back 1.25" or 30mm.  For a small amount of money, this is a HUGE difference in comfort and control


Handlebar riser for STOCK KTM 390 Adventure bars

Handlebar riser for STOCK KTM 390 Adventure bars


     Now let's get back to the best stuff, which is making and improving power delivery.   You can see a dyno run of our bike in stock condition below.  It's the lower of the 2 lines on both of the graphs.   This is on the stock tires at 25 psi.  


                               AND THEN TALK ABOUT THE REST OF THE OPTIONS.

    The upper line, is just the addition of our end cap.  There is NO reason to spend over $100 to make this muffler good. Our end cap makes the stock muffler make as much power as any of the expensive aftermarket mufflers.  We know, we tried those too


ktm exhaust vs stock.jpeg

     So you can see our high flowing endcap with it's 1.5" outlet hole, versus the stock 7/8" hole, which is also confined for a length of 4".  That's a lot of restriction.  The stock muffler has a straight through 1 7/8" core, so with the new end cap, you can easily understand how any high dollar muffler, isn't going to breath any better than this.

     You just drill out the stock rivets and remove the stock cap. Then install ours with the supplied torx screws.

And it's the only exhaust on the market, including the stock one, that can use an optional spark arrestor.  These bikes go in the brush and trees in the offroad areas too, so why no one want's to help keep you from lighting your area on fire, is just mind boggling.

KTM 390 Adventure Exhaust End Cap - Black

KTM 390 Adventure Exhaust End Cap - Black

$109.95Regular Price$99.95Sale Price

      After the exhaust was opened up and sounded better, there were a lot of things to try, to get the next best "bang for the buck"

      You can see from the pic below, that we tried the 2 main piggyback ecu's on the market. We also tried various "straight" through exhaust pipes and a thing called a "booster plug".   Also we tried various gearing changes.

      Here were the results we found, and then you can compare them to what others say, and more importantly "prove" with some science.  If you make changes without "proof of it being safe" , you may have a long walk home.


Booster plug for 2019-22 KTM 390 Adventure

Booster plug for 2019-22 KTM 390 Adventure


     You need to keep in mind, that the bike is designed to meet Euro 4 emissions standards. So it has 2 catalytic converters in the head pipe, and runs on the lean side.  It has an Oxygen sensor in the headpipe, for closed loop operation from idle to 7500 rpm, which means it trys to compensate for changes in fueling or airflow changes, and adjust to keep this 14.7 :1 air/fuel ratio.

    This is fine, but it also has a leaner area, from 2500 - 3000, where it runs about 15.2:1 AFR.  And this is the hesitation spot you feel off the bottom.  Adding the exhaust end cap is fine, because it doesn't accentuate it, and make the stumble worse, but other things like opening the airbox, or removing one or both catalytic converters, will cause the stumble to get worse and create a " not real safe" riding condition.

     The "Booster plug for KTM 390 Adventure" above, is the ONLY addition to the fuel ing options, that makes this better.  It's richens things up, just enough down there, to make the throttle control smoother and a little stronger.

14 tooth front sprocket for 390 Adventure

14 tooth front sprocket for 390 Adventure

Out of Stock


     Stock gearing is 15-45, and that is just to tall, for any kind of decent acceleration.   It's so much easier to switch the stock 15 tooth to a 14, than switch out the rear sprocket to a 48 or 49 tooth.    The front one, you can just change with the bike on the side stand.

     To change the rear, you'll have to buy a new chain.   The cost effectiveness and pure effectiveness,of just doing the front, makes it the final perfect addition.

     At this point it was tire time. I'm way more of an offroad guy than on road, and a lot of hills on my normal test route, I couldn't get up with the stock tires.

    I put some cost effective Shinko brand Trail adventure tires on it. They are the 805 and 804.  They are tubeless and I run 18 psi front and 20 psi rear, after some testing.

    They are as smooth on the road as the stock one, and so far have climbed all the hills the stock ones couldn't.

    For under $200 for both, I think it was a great choice and will use them again.  Plus they look manly tough

A skid plate, other than the plastic stock pile, should have been done by this time, especially with me having this obsession with wondering if I can break this bike. 

     Since nothing has been available that looked really good, we are working on our own design.  

     The folding, adjustable levers became a ( must have ) one day, when I crashed one day and the brake lever broke off.

     The brake lever was already a pain, because you couldn't adjust it close enough to the grip for smaller hands, so better levers where already on the way.

    But when the stock lever broke so fast, these became a must.

     Seems you can find a lot of these things on ebay and amazon, but none of those ever fit right, if they fit at all.

    These levers are pretty good and look pretty cool.

KTM 390 Adventure folding/adjustable levers

KTM 390 Adventure folding/adjustable levers

$74.95Regular Price$64.95Sale Price